GRB2 (human, P62993) curation notes

Identity and domain architecture

• 217-aa, ~25 kDa, non-catalytic adaptor: N-SH3 - SH2 - C-SH3; GRB2/sem-5/DRK family
  [file:human/GRB2/GRB2-uniprot.txt "Non-enzymatic adapter protein that plays a pivotal role in precisely regulated signaling cascades from cell surface receptors to cellular responses"].
• Isoform 2 (GRB3-3) lacks part of the SH2 domain, does not bind phosphorylated EGFR and acts as a dominant negative (UniProt isoform 2 FUNCTION).

Core molecular functions (with provenance)

1. SH2 phosphotyrosine recognition (GO:0001784).
2. EGFR: PMID:7518560.
3. IRS-1 / Shc: PMID:8491186; IRS-1 pY895 PMID:7504175.
4. BCR pY177 PMID:8112292.
5. FAK pY925 PMID:7597091; SHP2 pY584 PMID:8959326.
6. Specificity pY-x-N PMID:8663178.
7. SOS adaptor (GO:0005091). PMID:8386805; simultaneous SH2/SH3 occupancy PMID:7527391.
8. RTK adaptor bridging other effectors (GO:0005068). PI3K-C2beta PMID:11533253; Cbl PMID:23799367; HPK1 PMID:9346925; Tom1L1 PMID:19798056.
9. Immune signalosome adaptor (GO:0030674; TCR signalling). PMID:25870599; THEMIS/SHP1 PMID:25535246.
10. SH3 proline-rich recognition (GO:0070064). GAREM1 PMID:19509291; Spry2 PMID:16893902; Dab2 PMID:9569023.

Other biology (non-core)

• Homodimer; dimeric GRB2 restrains basal FGFR2 PMID:22726438; GAB1 binds GRB2 dimer PMID:22536782.
• Nuclear GRB2 in miRNA biogenesis PMID:37328606.
• Autophagy/BECN1 association PMID:38182563.
• NK cytotoxicity via DAP10 PMID:16582911.
• EGFR endocytosis PMID:14985334.

Curation decisions and rationale

GO:0005515 protein binding (564 rows; 162 papers; 207 partners)

Partners were resolved via UniProt REST. Decision was made per (paper, partner) after reading
each cached abstract (full text where needed):

• High-throughput studies (HuRI, HI-II-14, BioPlex 2/3, cell maps, MAPK Y2H, liver Y2H,
  ND network, SRM GRB2 dynamics PMID:21706016, PATS SH3 peptide arrays PMID:17474147, etc.)
  -> REMOVE. No binding mode or GRB2 activity is resolved per pair. Reason text notes when the
  partner is a known phosphotyrosine or SH3 partner and where the informative MF is captured.
• Small-scale, phosphotyrosine/SH2-dependent (EGFR, Shc, IRS-1, LAT, LAT2, LAX, BLNK,
  Kit, Axl, EphB1, SHP2, FAK, BCR, PTPalpha, PLD2, G6f, FCRL6, magicin pY64, TSPAN2 pY124)
  -> MODIFY to GO:0001784 phosphotyrosine residue binding.
• Small-scale, SH3/proline-rich motif mapped (GAREM1, Spry2, Dab2, GAB1 RXXK, HD-PTP,
  srGAP3, REPS2, ADAM15, 5-LO, WASP, HCV NS5A, p66Shc CH2 PPLP, Sos peptides in NMR/ITC)
  -> MODIFY to GO:0070064 proline-rich region binding. GO:0017124 SH3 domain binding is the
  reverse direction (it describes the ligand, not GRB2) and is not used. (The mouse Grb2
  review REMOVEd its SH3-ligand rows; here, where the motif is mapped, the informative MF is
  proposed instead. GO:0070064 is used for other SH3 proteins in human GOA, e.g. ABL1, BAIAP2, ITSN1.)
• SOS with adaptor evidence (Grb2-Sos bridging to phosphopeptides/receptors, Ras coupling)
  -> MODIFY to GO:0005091.
• GRB2 bridging an effector to an activated RTK (PI3K-C2beta, Gab2, Tom1L1, Cbl, HPK1,
  EGFR-Cbl mediator) -> MODIFY to GO:0005068.
• GRB2 bridging in LAT signalosome (THEMIS, SHP1; PTP1B-IRS-1 complex) -> MODIFY to GO:0030674.
• Everything else (co-IP without mapping, GRB2 as comparator in papers about Nck/Grap/Gads,
  abstracts not describing the GRB2 measurement) -> REMOVE with the standard caveat that removal
  does not mean the interaction is false.
• Special cases: PMID:9175774 (Shc peptide binds GRB2 SH2 regardless of phosphorylation) ->
  REMOVE rather than GO:0001784; PMID:16696976 (GRB2 N-SH3 inactive on dynamin endocytosis) -> REMOVE;
  PMID:9788432 WITH/FROM is MAP4K5/KHS, which the abstract says binds exclusively Crk proteins -> REMOVE;
  PMID:21725282 WITH/FROM is PTPRT but abstract concerns RPTPalpha -> REMOVE (noted).

Other notable calls

• GO:0045953 negative regulation of NK cell mediated cytotoxicity (IDA PMID:25870599) -> REMOVE:
  the full text (cached) is about CD4+ T cells and contains no NK or cytotoxicity data; GRB2 is a
  positive requirement in NKG2D-DAP10 cytotoxicity (PMID:16582911).
• GO:0017124 SH3 domain binding (IDA PMID:19509291) -> MODIFY to GO:0070064 (direction reversed).
• GO:0042802 identical protein binding -> MODIFY to GO:0042803 homodimerization for PMID:22536782
  and PMID:22726438; over-annotated for the SILAC pulldown (PMID:12577067).
• GO:0008180 COP9 signalosome (IBA/IDA/IEA) -> MARK_AS_OVER_ANNOTATED, consistent with mouse Grb2.
• GO:0007165 signal transduction IBA -> MODIFY to GO:0007265, consistent with mouse Grb2.
• GO:0003723 RNA binding (HDA) and extracellular exosome (HDA) -> MARK_AS_OVER_ANNOTATED.
• NEW: GO:0050852 T cell receptor signaling pathway (PMID:25870599). Participation: GRB2 is the
  adaptor that cross-links pLAT to effectors. Comparator: LAT and LCP2/SLP-76 carry GO:0050852 in GOA.
• 305 Reactome cytosol TAS rows and 8 plasma membrane TAS rows -> ACCEPT (correct locations).

Earlier independent review (PR #3319, Kit signaling module)

GRB2 was reviewed independently on main in PR #3319 while this review was in progress. When the MAPK_CASCADES branch was merged with main (2026-10-01), this review was kept as the canonical version because it re-types many bare protein-binding rows to informative terms where the earlier review removed them; its description and open questions were folded in where they added content. The earlier review's notes are preserved below for provenance (its deep-research file is in git history at commit 43395a519).

GRB2 curation notes

UniProt: P62993 (GRB2_HUMAN), 217 aa, HGNC:4566. Family: GRB2/Sem-5/DRK.
Architecture: N-terminal SH3 – central SH2 – C-terminal SH3 (SH3-SH2-SH3).

Core biology (synthesis)

GRB2 is a small, non-catalytic cytoplasmic signaling adaptor. It contains no
enzymatic activity; its function is entirely interaction-based. The central SH2
domain recognizes phosphotyrosine motifs (preference ~pY-x-N-x) on activated
receptor tyrosine kinases and phosphorylated scaffolds; the two SH3 domains bind
proline-rich motifs (PxxP / RxxK) on downstream effectors, chiefly the Ras GEF
SOS1/SOS2.

Canonical pathway: ligand activates an RTK -> RTK autophosphorylates -> GRB2 SH2
docks on receptor pTyr (directly, or indirectly via phosphorylated SHC1) -> GRB2
SH3 domains recruit SOS -> SOS placed at the plasma membrane loads GTP onto Ras
-> RAF-MEK-ERK (MAPK) cascade.

Key primary evidence:
- GRB2 links RTKs to Ras signaling; SH2 binds tyrosine-phosphorylated EGFR/PDGFR
PMID:1322798.
- GRB2 couples RTKs to a Ras guanine-nucleotide-exchange factor
PMID:8386805.
- Sos1 is a Ras GEF that binds GRB2 (UniProt RN[13], PMID:8493579).
- GRB2 (Ash/Grb-2) required for EGF/PDGF mitogenesis and actin/ruffle
reorganization [PMID:8253073 "The antibody abolished both S phase entry and the reorganization of actin assembly to ruffle formation upon stimulation with epidermal growth factor (EGF) and platelet-derived growth factor (PDGF)."; "Ash plays a critical role in the signaling of both pathways downstream from growth factor receptors to Ras and Rac"].

Adaptor/scaffold role beyond SOS-Ras:
- GRB2 nucleates LAT microclusters in TCR signaling; its SH3-ligand binding is
required for cluster formation, controlling PLCg1 activation and cytokine output
[PMID:25870599 "GRB2 regulates signaling downstream of adaptors and receptors by both recruiting effector proteins and regulating the formation of signaling complexes."; "GRB2, and its ability to bind to SH3 domain ligands, is required for establishing LAT microclusters"].
- Binds proline-rich motifs of partners via its SH3 domains, e.g. GAREM
PMID:19509291.
- Binds tyrosine-phosphorylated IRS1 (insulin/Ras coupling)
PMID:8388384.
- Binds activated EphB1 (ephrin receptor)
PMID:12925710.
- Homodimerizes (identical protein binding); dimeric GRB2 restrains basal FGFR2
signaling [PMID:22536782 "Grb2 exists in a monomer-dimer equilibrium"; PMID:22726438 "Dimeric Grb2 binds to the C termini of two FGFR2 molecules."].

Receptor endocytosis / signal termination:
- GRB2 is specifically required for clathrin-mediated EGFR endocytosis
PMID:14985334; it recruits CBL to activated EGFR (deep-research falcon, jiang2003 = internalization via CCPs).

Localization: predominantly cytosolic under basal conditions, translocating to
the cytoplasmic face of the plasma membrane on RTK activation; also detected at
endosomes during receptor trafficking, and nuclear GRB2 has been reported (miRNA
regulation, DNA-damage foci) [PMID:37328606 title "Regulation of microRNA expression by the adaptor protein GRB2."; PMID:21179510 nuclear/cytoplasmic HD-PTP colocalization].

Immune / other pleiotropic roles (non-core, downstream):
- NKG2D-DAP10 NK cytotoxicity requires a DAP10-bound Grb2-Vav1 intermediate
PMID:16582911.
- Node in a p21/ROS senescence signaling loop
PMID:20160708 -- treated as
peripheral/indirect (GRB2 does not itself carry out ROS metabolism or the DNA
damage response).

Curation decisions

• 564 x GO:0005515 protein binding (all IPI): REMOVE per CLAUDE.md policy. Generic
  protein binding is uninformative about GRB2's molecular function; removal does
  not dispute that the reported interactions occur. GRB2's actual adaptor function
  is captured by the specific MF terms (GO:0001784, GO:0005068, GO:0005091,
  GO:0030674, GO:0005154, GO:0043560, GO:0046875, GO:0019901, etc.).
• 307 x GO:0005829 cytosol (TAS Reactome + IDA/IEA): ACCEPT. Cytosol is a correct
  and well-supported basal location for this soluble adaptor; the large number of
  Reactome TAS rows is redundant provenance for the same, correct assertion.
• GO:0008180 COP9 signalosome: the IBA and IEA rows assert family-wide membership
  of the CSN (a GPS1/COPS1-8 complex) for an SH2/SH3 adaptor, which is
  biologically implausible; REMOVE those as over-propagation. The IDA (PMID:22561606)
  cites the Tespa1 paper whose abstract concerns the TCR signalosome, not the COP9
  signalosome; full text not available -> UNDECIDED (defer to curator, flag term).
• GO:0003723 RNA binding (HDA, interactome capture): KEEP_AS_NON_CORE -- real
  high-throughput identification, some corroboration from nuclear miRNA-regulation
  work, but not a core adaptor function.
• Specific RTK/partner binding (EGFR, TRKA, ephrin, IRS, kinase, phosphatase):
  ACCEPT the canonical/informative ones; KEEP_AS_NON_CORE the narrower partners.
• Pleiotropic BP (T/B/NK immune activation, myelination, Schwann cell dev,
  actin organization, Rac signaling, DNA damage/ROS/senescence, IGF pathway):
  KEEP_AS_NON_CORE.

No NEW annotations proposed: core molecular functions (phosphotyrosine binding,
RTK/GEF adaptor activity, protein-macromolecule adaptor activity) and their
processes (Ras signal transduction, MAPK cascade regulation, EGFR pathway,
receptor internalization) are all already present in the existing set.

Provenance for existing_annotations references

Deep research: genes/human/GRB2/GRB2-deep-research-falcon.md (Wang 2024
Biomolecules review; Malagrino 2024; Nocka 2023 eLife BTK; Qiu 2024 PNAS).